What is used to indicate that a surface must be machine finished?

• A. Finished marks
• B. Surface roughness symbol
• C. Datum
• D. Zone numbers

Answer: (A)

The surface roughness symbol is used to indicate that a surface must be machined to a controlled finish. This symbol, often paired with a numeric value (like Ra or other roughness metrics), tells the shop exactly how smooth the surface must be after finishing and confirms that machining, not just leaving the as-built surface, is required. Datum features establish a reference frame for tolerances and are not about surface texture, while zone numbers designate inspection areas rather than finish requirements. Although some older practices used “finished marks,” the standard and precise way to require a machine finish is with the surface roughness symbol.